In the communication channel, the transmitted signals simultaneously follow a multitude of different paths and are subject to reflection. Each receiving antenna receives a signal which is a superposition of a multitude of signals corresponding to this multitude of paths between the transmitter base and each receiver, such that interference phenomena occur which, in certain positions of a receiver antenna, can interfere with or cancel out the signal received by the receiver.
Transmission methods are known which use multi-carrier modulation, such as OFDM (for Orthogonal Frequency Division Multiplexing) which consists of multiplexing digital data onto frequency sub-carriers in order to transport the data on a communication channel. These sub-carriers are frequency-spaced and are orthogonal to each other to reduce interference.
At the same throughput as a single carrier modulation method, the signals have longer temporal durations and echoes in the communication channel have a reduced effect, meaning that there is less intersymbol interference (ISI) between consecutive symbols.
Although such multi-carrier methods are very advantageous, they do not completely cancel the interference problem, and it is common, for example, to add a guard space period between each symbol sent, which inevitably leads to a slower bandwidth.
However, bandwidth demand is constantly increasing, which means there is a need to reduce the time interval for digital data on the communication channel.